Hi Doublebubble, sorry that you are stressing over this, it is frightening when you don't have all of the information, so perhaps share your concerns with one of the midwives who will be able to reassure you somewhat.
I was the same as you, pfb son sleeping peacefully in his cot while I lay next to him, staring and worrying about having a midwife and, not one but two paediatricians, tell me that his testes were undescended. They were so matter of fact about it, and I was so shocked, that I didn't ask all of the questions that I would ask now and instead worried for days about whether this would lead to him being infertile, whether he would ever go through puberty, what other complications there could be, and my heart was breaking.
My son was referred to our local children's hospital for further examination, this scared my big time, but was actually only done as the two paediatricians, who were both training but didn't tell me that at the time, could not agree on what they were feeling at each examination. The specialist urologist that saw my son had no concerns, however agreed to follow up a year later anyway. We have been to the follow up check and all is fine. My husband and I could feel ourselves after a few months that both balls were in the sack, but the professional reassurance was such a relief after the initial worry.
I have a friend whose little boy had the same thing happen and he has to have a small operation to bring one of the testicles down as his tube is very tight, so it has been unable to descend on its own. The operation has been explained to her as short and routine, far more common than generally discussed (I suppose some people feel a stigma as bonkers as that is) and that they will be using a general anaesthetic for approximately 30 minutes. Her boy is now 18 months and on a waiting list. They generally don't do the operation whilst they are tiny / under 12 months, as it is not urgent or necessary to do so. However the doctor that my friend saw said that there are benefits to doing it at her son's sort of age up to 2 and a half as they are usually still in nappies and therefore can't pick their stitches and their recovery is good.
Sorry for the lengthy post, I just wanted to give you the information that I have in the hope that it brings some perspective of potential options. Particularly after seeing how unhelpful the first response that you received was - true or not it was insensitive.
Try to relax and get some sleep while baby is resting. Seek as much information as you can via midwives and health visitors. Don't feel that you have to bottle it all up, arm yourself with information and supportive people. (((Hugs)))